Microwave contactless coaxial connector



March 14, 1967 R. E. TRUDEAU MICOWAVE CONTACTLESS COAXIAL CONNECTOR Filed April 13, 1965 INVENTOR U W m W s w m Ra W T E. w w ,WA m f.

United States Patent Ofice 3,3%,632 Patented Mar. 14, 1957 3,309,632 MICROWAVE CONTACTLESS COAXIAL CONNECTOR Ronald E. Trudeau, Florence, Mass., assignor to Kolimorgan Corporation, Garden City, N.Y., a corporation of New York Filed Apr. 13, 1965, Ser. No. 447,701 8 Claims. (Cl. 333-33) This invention relates to a coaxial connector for use at microwave frequencies and more particularly to a make- 'break type choke coupler having no metal to metal contacts. The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

In the transmission and distribution of microwave signals from one point to another it is frequently necessary or desirable to be able to quickly connect or disconnect certain microwave transmission lines in a system. To be operationally useful, coupling or connector devices must provide a minimal amount of insertion loss and impedance discontinuity to the fiow of microwave signals. A known method of coupling one microwave transmission line to another makes use of an open quarter-wave transmission line section, called a choke, located at the discontinuity between the two lines to be coupled. Since the input impedance of an open quarter-wave choke section is zero, a microwave signal supplied to such a choke at the discontinuity between the coupled lines eifectively sees zero impedance and flows across the gap with minimal power loss.

The present invention provides a highly eicient, quickdisconnect microwave coaxial connector having an extremely low insertion loss and a low standing wave ratio even in the most hostile operational environments. Previously proposed quick-disconnect type microwave coaxial connectors require physical contact of mating metallic surfaces and therefore provide no adequate means for preventing contarnination of the metallic interfaces. Accordingly, they are vulnerable to the effects of hostile environments such as water, oil, corrosive vapors and the like, and consequently suffer degradation of transmission from exposure to such environments.

In accordance with a featured aspect of the present invention, each of the mating connector surfaces is completely encapsulated in a solid dielectric material to eliminate harmful effects of hostile environments on the connector.

In accordance with a further aspect of the invention, the separate choke couplers for the inner conductor and the outer shield respectively are longitudinally spaced to effectively eliminate undesired resonances within the operating bandwidth which might otherwise eXist through interaction of the individual chokes,

These and further objects and advantages of the present invention will be more readily understood when the following description is read in connection with the accompanying drawing in which:

FIG. 1 is a sectional view of a preferred embodiment of the microwave connector provided by the present invention showing the mating components of the connector in operational engagement; and

PIG. 2 is a sectional view of the connector made along the line 2-2 of FIG. l.

As illustrated, the two component fittings of the coaxial connector are shown in FIG. 1 in their fitted or coupled position with the interface between the two fittings indicated by line 10.

The first fitting 11 has a central inner conductor 12 and a surrounding outer cylindrical conductor 13. The two conductors of the first fitting are separated and held in a spaced relation by means of a solid polyethylene dielectric block molded in two pieces 14, 15. The outer conductor 13 is threaded as shown at 16 and 17 and a standard type N female termination 18 is shown threaded onto the first fitting. The external end of the dielectric block 15 is cut out at the region 19 of transition from coaxial air dielectric to that of polyethylene. The inner conductor 12 is advantageously tapered in the region indicated at 29 and the outer conductor is tapered at 21 to maintain a Constant line impedance while the inner conductor diameter increases. A step 22 is formed in the first inner conductor and a notch 23 :is cut in the first outer conductor to provide a mechanical locking feature within the assembly while at the same time maintaining uniform line impedance` The first inner conductor 12 is narrowed at the mating end of the first fitting and extends beyond the edge of the dielectric block for a distance equal to one-quarter wavelength at the microwave Operating frequency for which the coaxial connector is designed. The cross-section of the first outer conductor 13 of the fitting makes a transition from a broad shoulder 24 to a narrow protrusion 25 at the mating end of the first fitting. The mating end of the fitting is encapsulated so that a solid dielectric skin 2d of nominally .015 inch covers the connector interface.

The second fitting 27 of the coaxial connector comprises an inner conductor 28 surrounded by an outer conductor 29, the two being separated and held in spaced relation by two molded polyethylene blocks 30, 31. The outer conductor Z* is threaded at 32 and 33, and a standard type N female termination 34;- is shown connected to the end of the fitting. The dielectric block 31 is cut out in the region indicated by the numeral 3:5 where the transition from coaxial air dielectric to polyethylene takes place. Both the inner and outer conductors are tapered at 36 and 37, respectively, to maintain a uniform line impedance while the diameter of the inner conductor increases to permit the fabrication of the choke section to be described below. The inner conductor 28 is stepped at 38 and the outer conductor 29 has a notch at 39 to provide a mechanical looking feature within the assembly while maintaining uniform line impedance.

The mating end of the inner conductor 28 has a recess formed therein so that when the first and second fittings are brought together in mating relationship, the second inner conductor 23 receives the first inner conductor 12 and surrounds it for a distance of one-quarter wavelength. The dielectric filled recess R formed in the second inner conductor 28 extends a distance of approximately threequarters of a wavelength from the mating end of 28 to provide an effective open Circuit choke :termination at the design Operating frequency.

The mating end of ;the second outer conductor 29 has a first element 40 and a second element 41 both cylindrically surrounding and concentric with the second inner conductor 28. The first element 4% is separated from the second inner conductor 28, by a distance such that when the two fittings 11 and 27 are mated together and the second inner conductor 28 :receives the first inner conductor 12, the first element dt) fits closely about the encapsulated narrowed protrustion 25 of the first outer conductor 13 and surrounds the first outer conductor for a distance slightly less than one-quarter wavelength. The second element 41 is separated radially from the second inner conductor 28 by a distance greater than the radial separation of the first element 4G so that when the first and second fittings are mated |together, the second element 41 extends to the outer edge of the encapsulated shoulder portion 24 of the first outer conductor 13 and surrounds the narrowed protrustion portion 25 of the first outer conductor. In the embodiment shown, the first element dt) is fabricated separately from the second element 41 which is integral with the remainder of the second outer conductor 29. The two elements are brought together as shown in FIG. 1 and are in complete vmechanical and electrical contact. Polyethylene dielectric separates the two extending protrusions of the first and second elements, and the entire mating end of the second fitting 27 is encapsul'ated so that a solid dielectric skin 42 of nominally .015 inch covers the connector interfaces.

When the two fittings are fitted together so that the second inner conductor 28 receives and surrounds the first inner conductor 12 for one quarter wavelength, no D.-C. connection exists between the first and second inner conductors because of the encapsulating dielectric Skins 26 and 2 covering their mating surfaces, At the discontinuity between the first and second inner conductors, however, the described arrangement forms a choke consisting of a one-quarter wavelength coaxial line terminated in an open circuit, the excitation fields being rapidly attenuated in the region R beyond the choke section. Since an open circuited quarter-wavelength line has zero impedance at its input end, a very lo-w impedanee to the lmicrowave signal is placed at the discontinuity between the inner conductors.

Similarly, when the fittings are mated together as described above and shown in FIG. l, no D.-C. connection exists 'between the first and second outer conductors 13 and 29 because of the solid dielectric skin separating the conductors. The described arrangement, however, forms a choke section at the discontinuity between the two outer conductors. This choke :section is actually a onehalf wave-length line folded on itself and terminated in 'a short circuit 43 as shown. The short circuited halfwavelength line acts in the same manner as an open circuited quarter wavelength line to give a zero impedance at its input end, and since the discontinuity between the two outer conductors is located at this input end, a desired low microwave impedance is reflected at this point. This half wavelength section is so designed that the short circuit terminating the line at 43 occurs a quarter wavelength from a separation 44 in the choke body between the shoulder 24 of the first outer conductor 13 and the second element 41 of the second outer conductor 29. A short-circuited quarter wavelength line produces a very high impedance at its input so this arrangement places a very high impedance or a current minimum in the region of the separation 44, allowing the connector to be insensitive to 'the lack of D.-C. contact at the separation.

As illustrated in PIG. 1, the dimensions of the outer quarter wavelength section 45 'of the half Wavelength choke are advantageously made greater than those of the inner seotion 46, the outer section providing several times the impedance of the inner section to elfectively reduce the choke sensitivity to frequency Variation.

The microwave connector of the present invention is preferably constructed so that the discontinuities between the inner conductors at 48 and between the outer conductors at 49 are separated by approximately one quarter wavelength. This feature of the invention provides isolation |between the discontinuities and eliminates undesired resonances which could otherwise be produced by interaction between the inner and outer conductor choke couplers.

The conductor materials used in the connector may be any electrically conducting metal, such 'as stainless steel or brass. In the embodiment shown, a gold fiash over silver plating .GMB-.0005 inch thick was used to maintain high electrical conductivity. The dielectric material used is a medium density polyethylene, but Various types of plastics or other dielectric material may be selected to s'atisfy specific design requirements.

The microwave coaxial connector of this invention therefore provides a reliable make-break coupling with a quick-disconnect capability. Since the connector has been purposely constructed to prevent metal to metal contact of conductors by means of a dielectric separating the connector interfaces, the connector is not vulnerable to high refiection losses caused 'by contact contamination and shunting effects. As an example, such a ooaxial connector designed for S band operation had an insertion loss of less `than l db when the connector was operated submerged in salt brine. When the same connector was dripping wet with a combination of oil and salt water, its insertion loss did not exceed .5 d'b throughout its range of 2-4 gc.

It will be understood that various changes in the details, materials, steps and arrangement of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is clairned is:

1. A quick-disconnect microwave coaxial connector having a first fitting engageable with a second fitting, each of said fittings having an inner conductor and an outer conductor separated by dielectric material, said conductors having mating surfaces, the connector comprising:

(a) an open-circuited quarter-wavelength choke coupling the inner conductors,

(b) a short-circuited half-wavelength choke coupling the outer conductors, and

(c) two separable solid dielectric layers, each of said layers being bonded to the mating surfaces of the conductors of one of said fittings.

2. A quick-disconnect coaxial connector for use at a microwave frequency having a first fitting engageable with a second fitting, each of the fittings having an inner conductor and an outer conductor separated by a dielectric material, said conductors having mating surfaces, the connector comprising with the fittings engaged:

l(a) an open-circuited choke of one-quarter wavelength at the frequency coupling the inner conductors,

(b) a short-circuited choke of one-half wavelength at the frequency coupling the outer conductors, and

(c) two separable solid dielectric layers, each of said layers bein'g bonded to the mating surfaces of the conductors of one of said fittings.

3. A quick-disconnect microwave coaxial connector having a first fitting engageable with a second fitting, each of said fittings having `an inner conductor and an outer conductor separated by dielectric material, said conductors having mating surfaces, the connector comprising with the fittings engaged:

(a) an open-circuited quarter-wavelength choke coupling the inner conductors,

(b) a short-circuited half-Wavelength choke coupling the outer conductors,

'(c) a first pair of separable solid dielectric layers, each of said first pair of layers being bonded to the mating surfaces of one of the inner conductors of said fittingsfand (d) a second pair of separable solid dielectric layers, each of said second pair of layers being bonded to the mating surfaces of the outer conductors of said fittings. i

4. A quick-disconnect microwave coaxial connector having a first fitting en'gageable with a second fitting, each of the fittings having an inner conductor and an outer conductor separated by a dielectric material, said conductors having mating surfaces, the connector comprising with the fittings engaged:

(a) an open-circuited quarter-wavelength choke coupling at its input the inner conductors,

(b) a short-circuited half-wavelength choke coupling at its input the outer conductors, the input to the half-wavelength choke being distant from the input to the quarter wavelength choke by approximately onequarter wavelength, and

(c) two separable solid dielectric layers, each of said layers being bonded to the mating surfaces of the conductors of one of said fittings.

5. A quick-discounect microwave coaxial connector having a first fitting engageable with a second fitting, each of the fittings having an inner conductor surrounded by a cylindrical outer conductor, held in spaced relation by a dielectric material, said conductors having mating surA faces, the connector comprising With the fittings engaged:

(a) an open-circuited quarter wavelength choke coupling at its input the inner conductors,

(b) a short-circuited half waveiength choke coupling at its input the outer conductors, the half wavelength choke being formed in two-quarter wavelength sections of substantially different impedance, the input to the half wavelength choke lbeing distant from the input to the quarter wavelength choke by approximately one-quarter wavelength, and

(c) at least two separable solid dielectric layers, each of said layers being bonded to a conductor mating surface of one of said fittings.

6. A quick-disconnect coaxial connector for use at a microwave frequency comprising:

(a) a first fitting having a first inner conductor and a first outer conductor held in spaced relation from the first inner conductor by a first dielectric material, said conductors of said first fitting having mating surfaces;

(b) a second fitting adapted to be fitted together With the first fitting, said second fitting having a second inner conductor and a second outer conductor held in spaced relation from the second inner conductor by a second dielectric material, said conductors of said second fitting having mating surfaces;

(c) the first inner conductor extending from the first fitting a distance of one-quarter wavelength at said frequency, the second inner conductor having a recess formed therein so that when the first and second fittings are fitted together the second inner conductor receives the first inner conductor and surrounds the first inner conductor for a distance of one-quarter Wavelength at said frequency;

(d) the first outer conductor extending from the first fitting a distance of one-quarter wavelength at said frequency, the second outer conductor having' a first element extending from the second fitting a distance less than one-quarter wavelength at said frequency and a second element extending parallel to the first element from the second fitting a distance of onequarter wavelength at said frequency, so that when the first and second fittings are fitted together the first element surrounds the first outer conductor for a distance less than one-quarter wavelength at said frequency and the second element surrounds the first element and the first inner conductor for a distance of one-quarter wavelength at said frequency;

(e) two separable first solid dielectric layers, each of said first layers being bonded to the mating surfaccs of one of said inner conductors; and

(f) two separable second solid dielectric layers, each of said second layers being bonded to the mating surfaces of one of said outer conductors.

7. A quick-disconnect coaxial connector for use at a microwave frequency comprising:

cally surrounded by a first outer conductor, said first outer conductor held in spaced relation from the first inner conductor by a first dielectric material, said conductors of said first fitting having mating surfaces;

(b) a second fitting adapted to be fitted together with the first fitting, said second fitting having a second inner conductor cylindrically surrounded by a second outer conductor, said second outer conductor held in spaced relation from the second inner conductor by a second dielectric material, said conductors of Said second fitting having mating surfaces;

(c) the first inner conductor extending from the first fitting a vdistance of one-quarter wavelength at said frequency, the second inner conductor having a recess forrned therein so that when the first and second fittings are fitted together the second inner conductor receives the first inner conductor and surrounds the first inner conductor for a distance of one-quarter Wavelength at said frequency;

(d) the first outer conductor extending from the first fitting a distance of one-quarter wavelength at said frequency, the second outer conductor having a first element cylindrically surrounding and concentric with the aXis of the second inner conductor and extending from the second fitting a distance less than onequarter wavelength at said frequency and a second element cylindrically surrounding and concentric with the axis of the second inner conductor and extending parallel to the first element from the second fitting a distance of one-quarter wavelength at said frequency, so that when the first and second fittings are fitted together the first element surrounds the first outer conductor for a distance less than one-quarter wavelength at said frequency and the second element surrounds the first element and the first inner conductor for a distance of one-quarter wavelength at said frequency;

(e) two separable first solid dielectric layers, each of said first layers being bonded to the mating surfaces of one of said inner conductors; and

(f) two separable second solid dielectric layers, each of said second layers being bonded to the mating surfaces of one of said outer conductors.

8. The coaxial connector of claim 1 Wherein when the first and second fittings are fitted together the mating end of the first outer conductor is separated from the mating end of the second innerconductor by approximately onequarter wavelength at the Operating frequency.

References Cited by the Exaniiner UNITED STATES PATENTS 2,401,344 6/1946 Espley 333-97 X 2,434,509 1/1948 Okress 333-97 2,541,836 2/1951 Salisbury 333-97 3,089,105 5/1963 Alford 333-97 3,187,280 6/1965 Harrison 333-97 HERMAN KARL SAALBACH, Primary Examner.

R. HUNT, Assistant Examiner. 

1. A QUICK-DISCONNECT MICROWAVE COAXIAL CONNECTOR HAVING A FIRST FITTING ENGAGEABLE WITH A SECOND FITTING, EACH OF SAID FITTINGS HAVING AN INNER CONDUCTOR AND AN OUTER CONDUCTOR SEPARATED BY DIELECTRIC MATERIAL, SAID CONDUCTORS, HAVING MATING SURFACES, THE CONNECTOR COMPRISING: (A) AN OPEN-CIRCUIT QUARTER-WAVELENGTH CHOKE COUPLING THE INNER CONDUCTORS, (B) A SHORT-CIRCUITED HALF-WAVELENGTH CHOKE COUPLING THE OUTER CONDUCTORS, AND (C) TWO SEPARABLE SOLID DIELECTRIC LAYERS, EACH OF SAID LAYERS BEING BONDED TO THE MATING SURFACES OF THE CONDUCTORS OF ONE OF SAID FITTINGS. 